新型二維材料的熱動力學穩(wěn)定性及其電子結(jié)構(gòu)的調(diào)控
發(fā)布時間：2019-05-22 10:06
【摘要】：二維納米材料因維度受限而具有很多新奇的性質(zhì),已經(jīng)成為材料科學研究的前沿領(lǐng)域。最近,石墨炔(graphdiyne)和以單層黑磷(black-phosphorene)為代表的二維V族納米材料因所具有的優(yōu)異性質(zhì)引起了人們的巨大關(guān)注,隨著研究的不斷深入,逐漸展現(xiàn)出巨大的應(yīng)用潛力。為了拓寬以上兩類材料的應(yīng)用領(lǐng)域,且便于以它們?yōu)榛募{米器件設(shè)計,從理論角度深入研究石墨炔和二維V族納米材料的物理性質(zhì)顯得十分必要�；诖�,我們做了下述工作:1.采用分子動力學方法,并基于自適應(yīng)的分子反應(yīng)鍵序勢---AIREBO勢,我們系統(tǒng)地研究了單層石墨炔(graphyne和graphdiyne)在高溫下的演化行為。結(jié)果表明,在熔化過程中,單層石墨炔(graphyne和graphdiyne)將經(jīng)歷三個連續(xù)的相變。首先,單層的graphyne和graphdiyne分別從2800和2500 K時開始轉(zhuǎn)變成初始的無定形graphene相(AGP),簡稱為初相;接著,該初相會通過一結(jié)構(gòu)調(diào)整過程逐漸演化成無定形graphene相,這個過程一直會持續(xù)直至溫度升高到3650 K。該無定形graphene相會保持相對穩(wěn)定直到溫度進一步上升到大約5000 K;最后,當溫度進一步上升高于5000 K后,該無定形gaphene相會逐漸轉(zhuǎn)變成近似液態(tài)。單層graphyne和graphdiyne在高溫下的劇烈收縮和隨后的伸展在形成初始的無定形graphene相的過程中起了決定性的作用。不同于著名的KTHNY理論關(guān)于二維材料熔化的預(yù)測,在單層的graphyne和graphdiyne升溫的過程中,我們并沒有觀察到標志性的中間相---Hexatic相,而是無定形graphene相(AGP)。2.基于第一性原理計算,我們研究了以氫原子和羥基官能團(-OH)化學修飾graphyne和graphdiyne對它們結(jié)構(gòu)穩(wěn)定性的影響以及對它們電子結(jié)構(gòu)的調(diào)控效應(yīng)。(1)發(fā)現(xiàn)零點能在評估氫化graphyne的穩(wěn)定性時起重要作用�；谟嬎愕男纬伸�,我們發(fā)現(xiàn)僅存有sp2雜化的碳原子的graphyne氫化構(gòu)型(命名為eHH)比每個碳原子上只吸附一個氫原子的graphyne氫化構(gòu)型(命名為eH)更加穩(wěn)定。但是亥姆霍茲自由能與溫度的關(guān)系曲線表明,當溫度低于670 K時,eH比eHH更加穩(wěn)定。通過計算聲子譜,我們確定eH和eHH是動力學穩(wěn)定的氫化graphyne構(gòu)型。令人感興趣的是,graphyne的帶隙特征會隨著graphyne上氫原子覆蓋率的增加而經(jīng)歷一個直接到間接再到直接的轉(zhuǎn)變。(2)研究了羥基(-OH)修飾graphyne和graphdiyne的低能量構(gòu)型及其電子結(jié)構(gòu)。在高密度羥基修飾的低能量構(gòu)型中,由于羥基官能團間氫鍵的穩(wěn)定化作用,在相鄰的大三角碳環(huán)和六角碳環(huán)上羥基官能團會形成手性狀結(jié)構(gòu)。與氫化的graphyne和graphdiyne構(gòu)型相比,當羥基官能團把graphyne和graphdiyne中的碳碳鍵全部飽和成單鍵后的構(gòu)型是不穩(wěn)定的。結(jié)果還表明,羥基官能團在系統(tǒng)中可以導致磁性,但是這種磁性性質(zhì)只能存在于低羥基覆蓋率的構(gòu)型中。兩個羥基官能團間形成氫鍵的羥基對使系統(tǒng)一般不顯示磁性,這是因為兩個羥基在系統(tǒng)中導致的磁矩是反鐵磁耦合的。3.基于第一性原理計算預(yù)測了兩種新型孔狀二維碳同素異形體,命名為Cy和Cz。二者具有比graphdiyne更低的形成能。分子動力學模擬表明,即使溫度高于大約1000 K,Cy和Cz依舊可以保持其熱力學穩(wěn)定性。它們的泊松比顯示它們具有各向異性的力學性質(zhì)。電子結(jié)構(gòu)計算表明,Cy是一種金屬而Cz顯示為一種半導體。而且Cz具有各向異性的導電性,這表明了Cz在納米電子器件領(lǐng)域的應(yīng)用潛力。它們還具有特定尺寸且規(guī)律性分布的孔狀結(jié)構(gòu),有潛力成為新型的分子篩。4.基于第一性原理計算提出了三種具有奇異結(jié)構(gòu)和性質(zhì)的二維單層磷氮(PN)材料,分別命名為α-PN、β-PN和γ-PN。α-PN和γ-PN都具有彎曲的構(gòu)型,而β-PN則顯示出折疊的特征。它們的新奇構(gòu)型使這些單原子層的PN材料具有很高的熱動力學穩(wěn)定性及很強的各向異性的力學性質(zhì)。它們都是間接帶隙的半導體,而且它們的能隙對面內(nèi)的單軸應(yīng)變具有高度的敏感性。這三種單層的PN材料被裁剪成納米帶后呈現(xiàn)出顯著的量子尺寸效應(yīng)。尤其是,α-PN的鋸齒形納米帶顯示出依賴尺寸的鐵磁性。這些重要的性質(zhì)表明了它們在納米電子器件領(lǐng)域中應(yīng)用的潛力。我們還從理論上提出了實驗合成這三種PN單層相的可能途徑,這值得在實驗中進一步研究。5.基于聲子譜計算和有限溫度下的第一性原理分子動力學模擬,我們發(fā)現(xiàn)了一種新型的tricyle形的二維砷烯(arsenene),簡稱為T-As。T-As的結(jié)構(gòu)堅固且在較高溫度下仍可以保持熱力學穩(wěn)定。T-As的能量穩(wěn)定性可與先前報道的chair形arsenene(C-As)相比擬,且比stirrup形arsenene(S-As)更加穩(wěn)定。不同于C-As和S-As,單層的T-As是一種直接帶隙的半導體,其能隙為1.377 eV。我們的結(jié)果表明,通過堆垛、應(yīng)變、裁剪的方式都可以有效的調(diào)控T-As的電子性質(zhì),表明其在未來的納米電子器件領(lǐng)域具有應(yīng)用的潛力。而且,通過在T-As表面沿一個特定方向吸附氫或氟原子,可獲得具有特定邊緣類型以及寬度的納米帶,這有利于其被制成納米器件。
[Abstract]:The two-dimensional nano-material has many novel properties due to the limitation of the dimension, and has become the frontier field of material science research. Recently, the excellent properties of the two-dimensional V-group nano-material represented by the graphdiyne and the single-layer black-phosphorus are of great concern to the people, and with the development of the research, the great application potential is gradually displayed. In order to broaden the application field of the two kinds of materials, and to facilitate the design of the nano-devices based on them, it is necessary to study the physical properties of the graphene and the two-dimensional V-group nano-materials from a theoretical point of view. Based on this, we have done the following:1. The evolution behavior of graphynes and graphdiyne at high temperatures is systematically studied by means of molecular dynamics and based on the self-adapted molecular reaction-order potential--AIREBO potential. The results show that the single-layer graphne and graphdiyne will undergo three continuous phase transitions during the melting process. First, the single-layer graphye and gradiyne, respectively, began to transition from 2800 and 2500 K to the initial amorphous graphoene phase (AGP), which is simply referred to as the primary phase; then, the initial meeting gradually evolved into an amorphous graphene phase through a structural adjustment process, This process continues until the temperature is raised to a temperature of 3650 K. The amorphous graphenene meeting remains relatively stable until the temperature is further increased to about 5000 K; and finally, the amorphous gaphene meeting gradually turns into an approximately liquid state when the temperature is further increased above 5000 K. The severe shrinkage of the single-layer graphne and graphdiyne at high temperatures and the subsequent stretching play a decisive role in the process of forming the initial amorphous graphene phase. Unlike the well-known KTHY theory on the prediction of the melting of two-dimensional materials, we did not observe the iconic intermediate phase--the-----------------------the amorphous graphoene phase (AGP) in the process of temperature-raising of the single-layer graphyne and graphdiyne. Based on the first principle, we have studied the effect of the chemical modification of graphyne and graphdiyne on their structural stability by the chemical modification of hydrogen and hydroxyl functional groups (-OH) and the regulation effect on their electronic structures. (1) It is found that the zero point can play an important role in evaluating the stability of the hydrogenated graphyne. Based on the calculated formation rate, we have found that the graphyne hydrogenation configuration (named eHH) with only sp2-hybrid carbon atoms is more stable than the graphyne hydrogenation configuration (named eH) that adsorbs only one hydrogen atom on each carbon atom. But the relationship between the free energy and the temperature of Helmholtz shows that the eH is more stable than the eHH when the temperature is lower than 670 K. By calculating the phonon spectrum, we have determined that eH and eHH are kinetically stable hydrogenated graphyne configurations. It is of interest that the band gap characteristics of graphyne undergo a direct, indirect, to direct transition as the hydrogen atom coverage increases over the graphyne. (2) The low energy configuration and the electronic structure of graphye and graphdiyne modified by hydroxyl (-OH) were studied. In the low energy configuration of the high-density hydroxyl group modification, the hydroxyl functional groups on the adjacent large and hexagonal carbocyclic rings and the hexagonal carbon ring form a hand property structure due to the stabilizing effect of the hydrogen bond between the hydroxyl functional groups. The configuration of the carbon-carbon bonds in the graphyne and gram diyne as a single bond is not stable when the hydroxyl functional groups are fully saturated with the hydrogenated graphyne and graphdiyne configurations. The results also show that the hydroxyl functional groups can lead to magnetic properties in the system, but such magnetic properties can only be present in low hydroxyl coverage configurations. The hydroxyl group forming hydrogen bonds between the two hydroxyl functional groups makes the system generally not magnetic, because the magnetic moment caused by the two hydroxyl groups in the system is anti-ferromagnetic coupling. Based on the first principle, two new pore-like two-dimensional carbon allotype bodies, named Cy and Cz, are predicted, which have lower formation energy than graphdiyne. Molecular dynamics simulations show that Cy and Cz can still maintain their thermodynamic stability even if the temperature is above about 1000 K. Their poisson ratio shows that they have an anisotropic mechanical property. The calculation of the electronic structure shows that Cy is a metal and Cz is shown as a semiconductor. And Cz has an anisotropic conductivity, which shows the potential of Cz in the field of nano-electronic devices. They also have pore-like structures of specific size and regular distribution, and have the potential to be a new type of molecular sieve. Three-dimensional single-layer phosphorus-nitrogen (PN) materials with singular structures and properties are proposed based on the first principle. The two-dimensional single-layer phosphorus-nitrogen (PN) materials with singular structures and properties are named as P-PN, P-PN and P-PN, respectively. Both the I-PN and the P-PN have a curved configuration, and the P-PN shows the characteristics of the fold. Their novel configuration has a very high thermal dynamic stability and a strong anisotropy of the mechanical properties of the PN material of these single-atomic layers. They are both indirect band-gap semiconductors and their single-axis strain in the opposite direction has a high degree of sensitivity. The three single-layer PN materials are cut into nano-bands and exhibit a significant quantum-size effect. In particular, the saw-tooth nanoribbons of the p-pn exhibit a size-dependent ferromagnetic material. These important properties show the potential for their use in the field of nano-electronic devices. We also put forward the possible ways to synthesize these three kinds of PN single-layer phase from the theory, which is worth further study in the experiment. On the basis of the calculation of the phonon spectrum and the first principle molecular dynamics simulation at finite temperature, we have found a new type of tricle-shaped two-dimensional argenene, which is simply the structure of T-As. T-As and can still maintain the thermodynamic stability at higher temperatures. The energy stability of T-As can be compared with the previously reported chair-arsene (C-As) and more stable than that of the stirup-type arsene (S-As). Unlike C-As and S-As, a single-layer T-As is a direct band-gap semiconductor with an energy gap of 1.377 eV. Our results show that the electronic properties of T-As can be effectively controlled by stacking, strain and cutting, indicating the potential of application in the field of nano-electronic devices in the future. Moreover, by adsorbing hydrogen or fluorine atoms in a specific direction on the surface of the T-As, a nanobelt having a specific edge type and a width can be obtained, which is advantageous in that it is made into a nano-device.
【學位授予單位】：湘潭大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TQ127.11;TB383.1
本文編號：2482865
[Abstract]:The two-dimensional nano-material has many novel properties due to the limitation of the dimension, and has become the frontier field of material science research. Recently, the excellent properties of the two-dimensional V-group nano-material represented by the graphdiyne and the single-layer black-phosphorus are of great concern to the people, and with the development of the research, the great application potential is gradually displayed. In order to broaden the application field of the two kinds of materials, and to facilitate the design of the nano-devices based on them, it is necessary to study the physical properties of the graphene and the two-dimensional V-group nano-materials from a theoretical point of view. Based on this, we have done the following:1. The evolution behavior of graphynes and graphdiyne at high temperatures is systematically studied by means of molecular dynamics and based on the self-adapted molecular reaction-order potential--AIREBO potential. The results show that the single-layer graphne and graphdiyne will undergo three continuous phase transitions during the melting process. First, the single-layer graphye and gradiyne, respectively, began to transition from 2800 and 2500 K to the initial amorphous graphoene phase (AGP), which is simply referred to as the primary phase; then, the initial meeting gradually evolved into an amorphous graphene phase through a structural adjustment process, This process continues until the temperature is raised to a temperature of 3650 K. The amorphous graphenene meeting remains relatively stable until the temperature is further increased to about 5000 K; and finally, the amorphous gaphene meeting gradually turns into an approximately liquid state when the temperature is further increased above 5000 K. The severe shrinkage of the single-layer graphne and graphdiyne at high temperatures and the subsequent stretching play a decisive role in the process of forming the initial amorphous graphene phase. Unlike the well-known KTHY theory on the prediction of the melting of two-dimensional materials, we did not observe the iconic intermediate phase--the-----------------------the amorphous graphoene phase (AGP) in the process of temperature-raising of the single-layer graphyne and graphdiyne. Based on the first principle, we have studied the effect of the chemical modification of graphyne and graphdiyne on their structural stability by the chemical modification of hydrogen and hydroxyl functional groups (-OH) and the regulation effect on their electronic structures. (1) It is found that the zero point can play an important role in evaluating the stability of the hydrogenated graphyne. Based on the calculated formation rate, we have found that the graphyne hydrogenation configuration (named eHH) with only sp2-hybrid carbon atoms is more stable than the graphyne hydrogenation configuration (named eH) that adsorbs only one hydrogen atom on each carbon atom. But the relationship between the free energy and the temperature of Helmholtz shows that the eH is more stable than the eHH when the temperature is lower than 670 K. By calculating the phonon spectrum, we have determined that eH and eHH are kinetically stable hydrogenated graphyne configurations. It is of interest that the band gap characteristics of graphyne undergo a direct, indirect, to direct transition as the hydrogen atom coverage increases over the graphyne. (2) The low energy configuration and the electronic structure of graphye and graphdiyne modified by hydroxyl (-OH) were studied. In the low energy configuration of the high-density hydroxyl group modification, the hydroxyl functional groups on the adjacent large and hexagonal carbocyclic rings and the hexagonal carbon ring form a hand property structure due to the stabilizing effect of the hydrogen bond between the hydroxyl functional groups. The configuration of the carbon-carbon bonds in the graphyne and gram diyne as a single bond is not stable when the hydroxyl functional groups are fully saturated with the hydrogenated graphyne and graphdiyne configurations. The results also show that the hydroxyl functional groups can lead to magnetic properties in the system, but such magnetic properties can only be present in low hydroxyl coverage configurations. The hydroxyl group forming hydrogen bonds between the two hydroxyl functional groups makes the system generally not magnetic, because the magnetic moment caused by the two hydroxyl groups in the system is anti-ferromagnetic coupling. Based on the first principle, two new pore-like two-dimensional carbon allotype bodies, named Cy and Cz, are predicted, which have lower formation energy than graphdiyne. Molecular dynamics simulations show that Cy and Cz can still maintain their thermodynamic stability even if the temperature is above about 1000 K. Their poisson ratio shows that they have an anisotropic mechanical property. The calculation of the electronic structure shows that Cy is a metal and Cz is shown as a semiconductor. And Cz has an anisotropic conductivity, which shows the potential of Cz in the field of nano-electronic devices. They also have pore-like structures of specific size and regular distribution, and have the potential to be a new type of molecular sieve. Three-dimensional single-layer phosphorus-nitrogen (PN) materials with singular structures and properties are proposed based on the first principle. The two-dimensional single-layer phosphorus-nitrogen (PN) materials with singular structures and properties are named as P-PN, P-PN and P-PN, respectively. Both the I-PN and the P-PN have a curved configuration, and the P-PN shows the characteristics of the fold. Their novel configuration has a very high thermal dynamic stability and a strong anisotropy of the mechanical properties of the PN material of these single-atomic layers. They are both indirect band-gap semiconductors and their single-axis strain in the opposite direction has a high degree of sensitivity. The three single-layer PN materials are cut into nano-bands and exhibit a significant quantum-size effect. In particular, the saw-tooth nanoribbons of the p-pn exhibit a size-dependent ferromagnetic material. These important properties show the potential for their use in the field of nano-electronic devices. We also put forward the possible ways to synthesize these three kinds of PN single-layer phase from the theory, which is worth further study in the experiment. On the basis of the calculation of the phonon spectrum and the first principle molecular dynamics simulation at finite temperature, we have found a new type of tricle-shaped two-dimensional argenene, which is simply the structure of T-As. T-As and can still maintain the thermodynamic stability at higher temperatures. The energy stability of T-As can be compared with the previously reported chair-arsene (C-As) and more stable than that of the stirup-type arsene (S-As). Unlike C-As and S-As, a single-layer T-As is a direct band-gap semiconductor with an energy gap of 1.377 eV. Our results show that the electronic properties of T-As can be effectively controlled by stacking, strain and cutting, indicating the potential of application in the field of nano-electronic devices in the future. Moreover, by adsorbing hydrogen or fluorine atoms in a specific direction on the surface of the T-As, a nanobelt having a specific edge type and a width can be obtained, which is advantageous in that it is made into a nano-device.
【學位授予單位】：湘潭大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TQ127.11;TB383.1
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